The role and the interaction between RNA and proteins of the 30S ribosomal subunits in determining the ribosomal function will be studied. The approach is genetic, physiological and in vitro. Emphasis is given to the ribosomal function in controlling translational ambiguity, initiation of translation, and to ribosomal ability to discriminate transfer-RNAs. The repression of the arginine biosynthetic pathway will be studied in vitro, with particular emphasis on the study of the operator region.